This invention relates to an apparatus for forming seal liners within closure cap shells, and more particularly to the apparatus for applying resilient seal liners of foamed thermoplastic material, in particular polyethylene, to closure caps of the crown type for use in sealing bottles and the like.
It has been customary to apply cork liners to the crown type caps for sealing bottles and the like. However, the price of the natural cork is becoming more and more expensive. In addition, it is not very easy to firmly secure the cork liners within the cap shells. Thus, an attempt has been made to utilize resilient thermoplastic liners in place of cork liners, as disclosed in U.S. Pat. No. 2,654,913. Further, U.S. Pat. Nos. 3,135,019 and 3,360,827, disclose apparatus for producing seal liners by automatically depositing a measured charge of fused thermoplastic material without a foaming agent into each cap shell and then shaping the material into a seal liner by means of a molding plunger. However, the non-foamed thermoplastic seal liners thus obtained are inferior in cushioning and following properties as compared to natural cork liners and, therefore, have such a disadvantage that they occasionally cause an imperfect sealing effect. In order to eliminate the above disadvantage, an improved technique of making the seal liners of foamed plastics has been proposed, for example, in U.S. Pat. No. 3,265,785 to Rainer et al, in which the mixture of thermoplastic material and a foaming agent is fed into a cap shell and then roughly formed into a desired shape of liner by inserting a forming die or plunger into the cap shell, and then, after the plunger being removed, the roughly shaped liner is heated in order to activate the foaming agent contained beforehand in said mixture at free state (the state where the material is not pressurized by the plunger) by means of infrared-rays lamps or the like. However, according to the invention of Rainer et al, because the plastic material is foamed at free state, not only the cells in the foamed plastic are not uniform in size and distribution, but also uniform size and configuration of the formed liner cannot be obtained, these being very disadvantageous.
In order to overcome the above disadvantages, an improved method has been proposed in Japanese Patent Publication No. 48-19386 (corresponding to U.S. Ser. No. 846,027 filed July 30, 1969, W. C. Gwinner), in which a mixture of a thermoplastic resin composition and a heat activatable foaming agent is heated to activate the foaming agent and to furnish a heated, fused, foamed plastic mass, which is, in heated condition, deposited in a closure cap shell by means of an extruder, and then a cold or unheated molding die or plunger is applied under pressure to the deposited mass in the cap shell to mold a foamed seal liner. However, according to this method of Gwinner, because the mixture of the resin and the activated foaming agent is confined between the plunger and the cap shell, the produced gas is prevented from being discharged, causing irregular shapes of the formed liners.
In order to solve the above problem, the inventors of the present invention have proposed to provide a plurality of gas discharging bores in a single piece type forming die or plunger as disclosed in Japanese Laid-open No. 53-69786 of June 21, 1978 (Patent Applicaton No. 51-144383 filed Nov. 30, 1976). The plunger disclosed therein has such a lower cylindrical portion whose external diameter is equal to the internal diameter of a cap shell, the bottom surface of said lower cylindrical portion being formed with an annular groove or recess which is communicated with atmosphere through a plurality of inclined narrow gas discharging bores formed in the body of the plunger, wherein a mixture of thermoplastic polyethylene resin and a foaming agent is radially spread by the downward stroke of the plunger, and when the plunger takes its predetermined lowermost position, the resin is molded into a desired shape of the seal liner while the produced gas is discharged through the bores. However, there occurs such a problem that the narrow inclined bores are likely to be choked up and it is quite troublesome to remove the choking material out of each inclined bore. In addition, it is not easy to provide the narrow, inclined bores in the plunger body.
Further, it is known that, when thermoplastic resin in foamed by a foaming agent within a constant, pre-closed foaming space or room, produced cells of the seal liners are generally uniform in size and distribution. However, each of the above-referred forming dies or plungers disclosed in Japanese Patent Publication No. 48-19386 (U.S. Ser. No. 846,027) and Japanese Laid-open No. 53-69786 (Patent Application No. 51-144383) has such a construction that the flat central portion, which makes the charged resin radially spread and forms a thin disk-shaped central portion of the seal liner, and the annular recessed portion, which surrounds said flat central portion and forms a thicker annular pad portion of the seal liner, are integrally formed on a single piece of die or plunger, resulting in that the molding of the thin disk-shaped central portion of the liner and that of the thicker annular pad portion of the liner are simultaneously performed. Thus, in a strict sense, the molding of the thicker annular pad portion of the liner is not carried out under constant pre-closed condition. As a result, the cells in the thicker annular pad portion of the liner thus obtained are excessively large in size.
A seal liner molding device disclosed in U.S. Pat. No. 3,135,019 to Aichele was not intended to utilize foamed plastics. However, if foamed plastics be utilized with the Aichele device, it also has a disadvantage similar to that of the above referred Japanese Patent Publication No. 48-19386 and Japanese Laid-open No. 53-69786. The molding device of Aichele comprises a knife edged fender sleeve arranged so as to cover the side walls of the cap shell, an upwardly yieldable seal cushion die, and a punch for spreading a measured amount of thermoplastic material over and upon the interior surface of a cap shell, wherein the spreading application of the thermoplastic material by the punch operates to crowd a portion of the material toward the fender sleeve, resulting in that the material so forced is brought into engagement with the upwardly yieldable seal cushion forming die, whereby the material enters beneath and thrusts the die upwardly against tension of a spring acting upon the die, with the effect of providing the seal liner formation of a thickened annular cushion portion. However, if the thermoplastic material is foamed when the forming die is moved upward, it is impossible to provide a constant, closed space or room required for formation of uniform cellular organization in the seal liners. As a result, the cells in the seal liner thus obtained are not uniform in size and distribution.
It is, therefore, an object of the present invention to provide an improved apparatus for forming seal liners of foamed thermoplastic material within crown type cap shells which is capable of forming cells as uniform in size and distribution in the foamed seal liners by performing foaming operation within a constant closed foaming space or room.
Another object of the invention is to provide the seal liner forming apparatus having a movable die consisting of an inner cylindrical forming die or plunger and an outer, annular forming die, at least one of the two dies having a plurality of axially extending gas discharging grooves formed in its cylindrical slidable surface, the grooves being constructed and arranged for easy formation and maintenance (clearing), good efficiency in gas-discharging and easy prevention from being clogged up.
A further object of the invention is to provide the seal liner forming apparatus in which each outer annular forming die is so arranged that when it takes the lowermost position, a clearance between the bottom end surface of the die and an interior surface of a cap shell is always constant.
A still further object of the invention is to provide the seal liner forming apparatus which permits desired uniformity in cellular organization of the formed seal liner as well as efficiency in mass-production by regulating formation of cellular organization in the seal liner by simultaneously cooling the movable die and the stationary die which supports the underside of a cap shell.
A further object of the invention is to provide the seal liner forming apparatus which permits mass-production and uniform quality of the seal liners, by provision of a cooling water flow regulating means operable in accordance with temperature, operating time and other operating conditions when the movable forming die and the stationary die are cooled down.
Other objects, features and advantages of the invention will become apparent from the detailed description given hereinbelow in connection with the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.